Method of operating compression type refrigeration system



United States Patent US. Cl. 252-68 3 Claims ABSTRACT OF THE DISCLOSURE A refrigeration system of the closed hermetically sealed compression type is-operated with dichlorodifluoromethane as a refrigerant, a mineral oil as a lubricant and ethylenediamine tetracetic acid or a salt thereof as an additive for inhibiting reaction between the refrigerant and the oil.

BACKGROUND OF THE INVENTION In hermetically sealed refrigeration systems, in which the oil and refrigerant are in direct heat exchange relationship with each other, the maximum operating temperature of the refrigeration compressor is often limited by the chemical instability of the oil-refrigerant mixture. A

refrigerant commonly used in hermetically sealed systems is dichlorodifluoromethane (R12) while various petroleum oils are employed as lubricants. When tested independently, both the refrigerant and the oil are stable for the expected operating life of the equipment at temperatures well above those which are normally attained in actual operation. However, it has been known for some years that when mixed the refrigerant R12 and petroleum oils react at moderately elevated temperatures and that the reaction may result in the formation of carbon or coke deposits. It is also known that the rate of reaction is accelerated in the presence of iron or steel and that steel valve plates are particularly susceptible to coking at elevated temperatures. Since the refrigerant R12 is soluble in petroleum oils and since the solution comes in direct contact with various components of the compressor which are made from steel, it is highly desirable to provide means for preventing or reducing the R12-mineral oil reaction. Various attempts to improve the stability of the R12-oil working fluids at elevated temperatures have included the use of highly refined mineral oils free of activating impurities which might accelerate or initiate the R12-oil reaction, and the use of various additives of the type found to be useful in improving the stability of lubricity of lubricants in fields outside the refrigeration field. How ever, such conventional lubrication additives have not been found to be particularly effective in inhibiting or preventing the R12-oil reaction and, in fact, it is well known, as shown for example by the discussion of this problem in US. Pat. No. 2,824,061-Davidson et a1. issued Feb. 18, 1958, some of them may actually lower the critical reaction temperature at which the R12-oil reaction takes place within a refrigeration system. The Davidson et al. patent is directed to the use of certain alkali metal salts of phosphoric acid esters to inhibit the degradation of the oil and/ or refrigerant.

SUMMARY OF THE INVENTION The present invention is based on the discovery that polyaminocarboxylic acids and various sodium salts thereof, added to the oil-refrigerant working fluid in the system, are particularly effective in inhibiting the R12-oil reactions in refrigerating ssytems.

DESCRIPTION OF THE PREFERRED EMBODIMENTS More specifically, in accordance with the present inven- 3,532,631 Patented Oct. 6, 1970 ice.

wherein X is a monovalent radical selected from the class consisting of hydrogen and alkali metals. Specific examples of such compounds are ethylenediamine tetraacetic acid, ethylenediamine tetraacetic acid disodium salt and ethylenediamine tetraacetic acid tetrasodium salt. Typically, these compounds are iron chelating agents, well-known by those skilled in the art. While solubility in the refrigerant-oil mixture may increase effectiveness of the metal complexing agent, this is not a necessary requirement, as will be demonstrated.

The effectiveness of a representative agent in inhibiting the R12-oil reaction is demonstrated by the following tests.

A series of sealed tubes were prepared containing 1.45 g. of R12 (pretreated to reduce R22 impurity), 1 cc. of a highly refined parafllnic mineral oil with 1% tricresylphosphate and additional materials as shown in Table I. These combinations of materials simulate the environment at the peak temperature areas in the refrigerator compressor with the tricresylophosphate additive accelerating any oil-refrigerant reaction thereby providing shorter periods of test. The sealed tubes were aged for two weeks at C. and the contents analyzed by gas chromatography for R12 decomposition which is known (H. O. Spauschus and G. C. Doderer, ASHRAE Journal 3, No. 2, 65, 1961) to involve the formation of monochlorodifluoromethane (R22) in accordance with the following type of reaction:

TAB LE I Additional materials 1, 2 0.05 g. valve steeL 1, 670,

5, 6 50 p.p.m. soluble iron in oil 960,

7, 8 0.05 g. valve steel-0.0025 g. of an aqueous 960, solution (50%) of tetrasodium of ethylenediamine tetraacetic acid.

9, 10-....- 0.05 g. valve steel-0.0014 g. of the tetrasodium salt of ethylenediamine tetraacetic acid in bead form.

Tubes However, it is also believed that the rate of solution of the iron in the working fluid decreases with time; possibly due to a gradual alteration of the chemical activity of the steel surfaces within the system. Accordingly, a minimum percentage of, for example, 0.1% by weight of the oil of the aminocarboxylic acid salt additive will provide an effective inhibition of the oil-refrigerant reaction in the system. In general no significant advantage is obtained by employing more than about 0.5% by weight of the aminocarboxylic acid salt additive based on the weight of the oil although it is obvious that this percentage may be exceeded when the additive is in a bead-like form in which most of the effectiveness of the solid material is dependent upon the exposed surface area of the beads.

While the invention has been described particularly in the connection with certain specific additives, it is ob vious that it is not limited thereto and that various modifications can be made without departing from the spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In the method of operating the refrigeration system of the hermetically sealed, compression type employing dichlorodifiuoromethane as a refrigerant and a min eral oil lubricant in contact with said refrigerant, the improvement which comprises operating said refrigeration system with the addition to the system of at least 0.1 percent by weight of a compound of the formula XOOCHZC CHzCOOX XOOCHzC CHsCOOX wherein X is a monovalent radical selected from the class consisting of hydrogen and alkali metals said compound being effective to inhibit reaction between said oil and said refrigerant in the presence of steel.

2. The method of operating a refrigeration system as defined in claim 1 in which said compound is a sodium salt of ethylenediamine tetraacetic acid.

3. The method of operating a refrigeration system as defined in claim 1 in which said compound is added to the compressor lubricant in the system.

References Cited UNITED STATES PATENTS 2,552,084 5/1951 Bishop et a1. 3,129,185 4/1964 Rizzuti et a1. 3,375,197 3/1968 Spauschus et al.

RICHARD D. LOVERING, Primary Examiner US. Cl. X.R. 6285 

